Attainable region analysis for continuous production of second generation bioethanol

Abstract

BackgroundDespite its semi-commercial status, ethanol production from lignocellulosics presents many complexities not yet fully solved. Since the pretreatment stage has been recognized as a complex and yield-determining step, it has been extensively studied. However, economic success of the production process also requires optimization of the biochemical conversion stage. This work addresses the search of bioreactor configurations with improved residence times for continuous enzymatic saccharification and fermentation operations. Instead of analyzing each possible configuration through simulation, we apply graphical methods to optimize the residence time of reactor networks composed of steady-state reactors. Although this can be easily made for processes described by a single kinetic expression, reactions under analysis do not exhibit this feature. Hence, the attainable region method, able to handle multiple species and its reactions, was applied for continuous reactors. Additionally, the effects of the sugars contained in the pretreatment liquor over the enzymatic hydrolysis and simultaneous saccharification and fermentation (SSF) were assessed.ResultsWe obtained candidate attainable regions for separate enzymatic hydrolysis and fermentation (SHF) and SSF operations, both fed with pretreated corn stover. Results show that, despite the complexity of the reaction networks and underlying kinetics, the reactor networks that minimize the residence time can be constructed by using plug flow reactors and continuous stirred tank reactors. Regarding the effect of soluble solids in the feed stream to the reactor network, for SHF higher glucose concentration and yield are achieved for enzymatic hydrolysis with washed solids. Similarly, for SSF, higher yields and bioethanol titers are obtained using this substrate.ConclusionsIn this work, we demonstrated the capabilities of the attainable region analysis as a tool to assess the optimal reactor network with minimum residence time applied to the SHF and SSF operations for lignocellulosic ethanol production. The methodology can be readily modified to evaluate other kinetic models of different substrates, enzymes and microorganisms when available. From the obtained results, the most suitable reactor configuration considering residence time and rheological aspects is a continuous stirred tank reactor followed by a plug flow reactor (both in SSF mode) using washed solids as substrate.

Kinetic Modeling of 1‐G Ethanol Fermentations

“…• Scott et al [73]: Attainable region analysis for continuous production of second-generation bioethanol.…”

A generalized disjunctive programming framework for the optimal synthesis and analysis of processes for ethanol production from corn stover

“…Since a large number of the conceivable process configurations that can be obtained from the 2 28 possible combinations of the Boolean variables will not define feasible topologies, it is necessary to introduce a set of logic propositions relating the Boolean variables (ષሺሻ = ‫. )݁ݑݎܶ‬ Logic arguments can be incorporated to the superstructure by using the logical operators OR (∨), AND (∧), IF-THEN (⇒), XOR (exclusive or, ∨ ), NOT (¬) and IF AND ONLY IF (⇔).…”

“…However, a thorough comparison between process configurations is not possible due to an inexistent common framework of economic parameters and pretreatment conditions. Using the Attainable Region concept, Scott et al (2013) showed that for the saccharification and fermentation of PCS the reactor networks that minimize the residence time can be constructed using plug flow reactors and continuously stirred tank reactors, despite the complexity of the reaction networks and underlying kinetics. However, no solid separators were included in this analysis.…”

Optimal Pathways for Nitric Acid Synthesis Using P-Graph Attainable Region Technique (PART)

“…Though this semi-commercial process is able to produce bioethanol from unwanted biomass, it still requires optimisation and improvement to achieve economic success [13]. With this in mind, some researchers have employed AR techniques to analyse and improve the effectiveness of the bioreactor configuration to boost the production of bioethanol [14].…”